<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>025-显示转换下.html</title>
</head>
<body>
	
</body>
<script>
	var a = undefined;

	console.log("a:::",a);
	console.log(typeof a);

	var b = Number(a);
	console.log("b:::",b);
	console.log(typeof b);
</script>
</html>